Primary Collection of Cheats
Do the following to get access to a cheats menu with options like invulnerability, all weapons, all items, infinite ammo, level select, and many more.
Under the installed folder in the path DATA\SCRIPTS\MENUS\ENGLISH are three files: E3.MSC, DEBUG.MSC, AND RELEASE.MSC. Rename RELEASE.MSC to something like RELEASE.MEN, then copy DEBUG.MSC to RELEASE.MSC in this same folder.
Now, when the game is started, there will be added menus where many extra options can be set.